Blended wing body aircraft are known in which the fuselage and wings are integrated such that there is no clear dividing line between the wings and fuselage. The body may therefore contribute to lift, increasing the efficiency of the aircraft. In a “flying wing” design, the fuselage is omitted, with the pilot, passengers and engines provided within the wing.
One known blended wing body study is described in Liebeck, R. H. “Design of the Blended Wing Body Subsonic Transport.” AIAA Journal of Aircraft, Volume 41, Issue 1, January-February 2004, pp. 10-25. Blended wing body and flying wing configurations are also known in which the engines are mounted within the wing (such as the Northrop B2). Trade studies have shown that such a design is most suitable for relatively large, long range aircraft.
Gas turbine engines are highly efficient, and have high thrust to weight ratios. However, some failure modes of gas turbine engines can cause extensive damage to safety critical aircraft components such as other engines, fuel tanks, hydraulic and electrical control runs, and aircraft propulsors in the case of a distributed propulsion aircraft. For example, the uncontained rupture of a compressor or turbine rotor disc can, in some cases, lead to the destruction of adjacent engines, fires in fuel tanks, or severance of hydraulic or electrical control runs, which may lead to loss of control. Consequently, in most conventional aircraft, the engines are spaced far apart (either by locating engines spaced on the wing, or by locating one or more engines in the tail of the aircraft) and physically distant from safety critical aircraft components, thereby reducing the risks of damage to other safety critical aircraft components in the event of an uncontained disc rupture event. Alternatively, the engines may be surrounded by relatively heavy and expensive containment structures to prevent uncontained failures from occurring.
However, it is desirable to locate both the wings and engines close to the centre of mass of the aircraft, since the engines represent a large proportion of the mass of the aircraft, and locating the wings (and so the centre of lift) close to the centre of mass reduces trim drag which would otherwise be necessary to cancel the torque produced in flight by the centre of lift/centre of mass mismatch. If the engines are installed within the fuselage, this leads to engines close to one another, as well as close to fuel tanks in the wings, and hydraulic and/or electrical control runs which pass from the cockpit to the aft of the aircraft. Such an arrangement, while aerodynamically and structurally efficient, leads to unacceptable aircraft risks in the event of an uncontained disc failure.
The present invention describes an aircraft which seeks to overcome some or all of the above problems.